Nonmetallic process connection

0001This application claims benefit of provisional application 60/545,156, filed Feb. 17, 2004.

BACKGROUND

00021. Technical Field

0003This invention relates to process control systems, and more particularly to noninvasive toroidal-type conductivity sensors.

00042. Background Information

0005Throughout this application, various publications, patents and published patent applications may be referred to by an identifying citation. The disclosures of the publications, patents and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure.

0006Flow-through electrodeless conductivity sensors are commonly used to measure various parameters of fluids flowing through a manufacturing process. For example, the 871FT™ Conductivity Sensors (Invensys, PLC) are commercially available non-invasive assemblies suitable for a broad range of conductivity and concentration measurement applications. These 871FT sensors are currently available in several line sizes from ½ inch up to 4 inch. They offer a wide choice of wetted parts materials and end connections, including both industrial and sanitary types.

0007Unlike conventional insertion type sensors, these flow-through sensors are integrated with the process piping, to provide for conductivity measurement in a non-invasive manner. Self-cleaning is provided due to the tubular design geometry. Calibration of the 871FT sensors may be accomplished in-line through use of a built-in calibration port. In-line calibration is beneficial in applications that use aggressive chemicals and others (e.g., pharmaceuticals) in which opening the process line is undesirable due to concerns of potential contamination.

0008The 871FT sensors may use an optional temperature detector (e.g., Resistive Temperature Detector (RTD)) for automatic temperature compensation. These sensors are compatible with conventional data transmitters and analyzers for use in factory automation networks.

0009The 871FT sensors rely on metallic end connections to provide electrical continuity with the process solution in order to generate the desired conductivity data. These metallic portions, however, generally render the sensors unsuitable for use in many applications, such as those that use highly corrosive process solutions. For example, corrosive agents commonly used in semiconductor fabrication processes as etchants, such as HF (Hydrofluoric) Acid, are highly reactive with, and thus tend to corrode, metallic components.

0010These conventional sensors tend also to be incompatible with many high purity processes which may be particularly sensitive to contamination from metals.

0011Thus, a need exists for an improved flow-through electrodeless sensor suitable for use in highly corrosive environments and/or in environments that demand a relatively high degree of purity.

SUMMARY

0012One aspect of the invention includes a sensor having a toroid assembly of primary and secondary toroids disposed in spaced, coaxial relation to one another with a process flow path extending through the assembly. Electrically conductive and non-metallic connectors are located at opposite ends of the flow path. The primary toroid is configured to induce an electric current in the process fluid as the process fluid passes through the flow path, wherein the current varies with conductivity of the process fluid. The secondary toroid is configured to detect the electric current in the process fluid as the process fluid passes through the flow path, the current being proportional to the conductivity of the process fluid.

0013Another aspect of the invention is similar to the foregoing aspect, while also including a signal port for connecting the toroid assembly to a process variable transmitter. In addition, an electrically non-conductive housing defines the flow path and the connectors are configured for disposition in physical contact with the process fluid flowing therethrough.

0014A further aspect of the invention includes a method for fabricating a toroidal fluid conductivity sensor, the method includes placing primary and secondary toroids in spaced, coaxial relation to one another, extending a process flow path through the toroids, and placing first and second non-metallic electrically conductive connectors at opposite ends of the flow path. The method also includes configuring the primary toroid to induce an electric current in the process fluid, and configuring the secondary toroid to detect the current in the process fluid as the process fluid passes through the flow path, the induced current being proportional to the conductivity of the process fluid.

0015A still further aspect of the invention includes a method for measuring the conductivity of a fluid. The method includes providing the sensor of the first aspect of the invention described above, coupling the connectors in series with a fluid flow conduit, and electrically coupling the electrically conductive non-metallic connectors to one another. The method further includes inducing, with the primary toroid, an electric current in process fluid passing through the sensor, and detecting, with the secondary toroid, the current in the process fluid as the process fluid passes through the sensor, the current being proportional to the conductivity of the process fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

0016The above and other features and advantages of this invention will be more readily apparent from a reading of the following detailed description of various aspects of the invention taken in conjunction with the accompanying drawings, in which:

0017<figref idref="DRAWINGS">FIG. 1</figref> is an elevational schematic view, with portions broken away, of an embodiment of the present invention in a representative installation;

0018<figref idref="DRAWINGS">FIG. 2</figref> is an elevational schematic view, on an enlarged scale, of an embodiment of the present invention;

0019<figref idref="DRAWINGS">FIG. 3</figref> is a view similar to that of <figref idref="DRAWINGS">FIG. 2</figref>, of an alternate embodiment of the present invention; and

0020<figref idref="DRAWINGS">FIG. 4</figref> is an elevational schematic view, with portions broken away, and portions shown in phantom, of portions of an embodiment of the present invention.

DETAILED DESCRIPTION

0021In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized. It is also to be understood that structural, procedural and system changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents. For clarity of exposition, like features shown in the accompanying drawings shall be indicated with like reference numerals and similar features as shown in alternate embodiments in the drawings shall be indicated with similar reference numerals.

0022Turning now to <figref idref="DRAWINGS">FIG. 1</figref>, an exemplary embodiment of the present invention, sensor <b>20</b>, is shown in a typical installation, within a fluid process conduit <b>21</b>. Process solution flows through the conduit <b>21</b> and through sensor <b>20</b>, in a downstream direction indicated by arrow a.

0023Turning to <figref idref="DRAWINGS">FIG. 2</figref>, sensor <b>20</b> includes many components common to a conventional 871FT Conductivity Sensor, including a toroid assembly <b>22</b>, an output cable <b>24</b> for connection to a conventional process variable transmitter and/or analyzer <b>46</b> (<figref idref="DRAWINGS">FIG. 4</figref>), a non-metallic insulator <b>26</b>, and optionally, an integral probe <b>28</b>, such as a temperature detector.

0024Referring to <figref idref="DRAWINGS">FIG. 4</figref>, sensor <b>20</b> operates in a conventional manner, such as described in U.S. Pat. No. 5,157,332. As shown, primary and secondary inductive toroids <b>40</b> and <b>42</b>, respectively, are mounted in the toroid assembly <b>22</b> coaxially with a flow path defined by a housing <b>44</b>. Additional toroids, such as additional primary toroid <b>40</b>′ shown in phantom, may be optionally provided, such as to enhance various operational characteristics.

0025The primary toroid(s) induce an electric current in the process fluid as it passes therethrough. The voltage created, which varies with process fluid conductivity, is detected by the secondary toroid and converted to a conductivity measurement. Advantageously, the smooth bore through toroid assembly <b>22</b> enables sensor <b>20</b> to provide a noninvasive measurement of conductivity. An optional temperature sensor <b>28</b> (<figref idref="DRAWINGS">FIG. 2</figref>) may be used to compensate the conductivity measurement for the temperature of the process fluid.

0026Turning now to <figref idref="DRAWINGS">FIGS. 2 and 3</figref>, end connectors <b>30</b>, <b>30</b>′ disposed at opposite ends of housing <b>44</b>, couple the housing in series within flow conduit <b>21</b> (<figref idref="DRAWINGS">FIG. 1</figref>). These end connectors (also referred to as process fittings) <b>30</b>, <b>30</b>′ are also electrically conductive, and in the embodiments shown, are non-metallic. Their electrical conductivity enables connectors <b>30</b>, <b>30</b>′ to provide electrical continuity with the process solution to facilitate generation of the desired conductivity data. The connectors at both ends are electrically coupled to one another, such as with a cable <b>33</b>, to provide a complete electrical circuit, to facilitate accurate conductivity measurement. In addition, the non-metallic nature of connectors <b>30</b>, <b>30</b>′ enables them to be used with process solutions that are generally incompatible with metals or applications which may be sensitive to metallic contamination.

0027For example, sensors <b>20</b>, <b>20</b>′ thus may be used in semiconductor fabrication processes that use HF acid or other caustic fluids as etchants, etc. Sensors <b>20</b>, <b>20</b>′ may also be used in high purity, sanitary applications which may be sensitive to metal contamination.

0028Exemplary connectors <b>30</b>, <b>30</b>′ may be fabricated from electrically conductive (carbon-impregnated, for example) polymers such as PTFE (e.g., TEFLON®, DuPont), Fluorine-containing synthetic resins (e.g., KYNAR®, Atofina Chemicals, Inc.), PEEK, and other conductive plastics. In the particular embodiment shown, connectors <b>30</b> are provided with exterior threads to facilitate coupling to conventional piping systems <b>21</b>. Moreover, although carbon is impregnated into these non-metallic materials to provide the desired conductivity, those skilled in the art should recognize that substantially any non-metallic conductive material that may be currently available or developed in the future, may be used without departing from the spirit and scope of the present invention.

0029Turning specifically to <figref idref="DRAWINGS">FIG. 3</figref>, an alternate embodiment of the invention, shown as sensor <b>20</b>′, is substantially similar to sensor <b>20</b>, though instead of external threads, uses connectors <b>30</b>′ having terminal flanges <b>32</b> for coupling to mating flanges of piping system <b>21</b>.

0030These flanged connectors <b>30</b>′ are useful, for example, in conventional sanitary applications. Although shown without it in this Figure, sensor <b>20</b>′ may be used with or without optional temperature detector <b>28</b> (<figref idref="DRAWINGS">FIG. 2</figref>).

0031Although embodiments of the subject invention have been shown and described having threaded and flanged connections, those skilled in the art should recognize that connectors configured in substantially any manner capable of coupling to a process fluid connection may be used, including for example, but not limited to, those commonly known as Tri-clamp, sanitary, flange, pipe (e.g., threaded) fitting, hose and tube connections, etc., without departing from spirit and scope of the present invention.

0032Moreover, although embodiments of the instant invention have been shown and described in the context of a modified 871FT toroidal sensor, the skilled artisan should recognize that nominally any type of toroidal conductivity sensor may be used in combination with conductive non-metallic connectors as described herein, without departing from the spirit and scope of the present invention.

0033In the preceding specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.